8 
FOSSIL REPTILIA OF THE 
surface posteriorly for the intervertebral substance and a small part of the succeeding 
centrum, where a slight expansion of the everted border of the articular surface is 
the sole indication of such hsemapophysial junction. In the terminal vertebrge these 
surfaces with the haemapophyses have disappeared, and the centrum, now showing a 
compressed form, supports only a contraeted, anehylosed, seemingly exogenous neural 
areh, wdrich finally disappears. 
The following are transverse diameters of the centrum in different regions of the 
spine, in the specimen, 8 feet 9 inches long, of Plesiosaurus (hlicJiodeirus, figured in 
Tab. I : 
In. lines. 
Tenth cervical vertebra ....... 1 0 
Middle dorsal ditto ........ 2 0 
Tenth caudal ditto ........ 1 .3 
Cranial characters (Tabs. II and III). 
The skull in this skeleton presents, what is rare, the side or profile view (Tab. II) 
like that of the succeeding anterior cervicals. Its upper part is mueh injured. The 
following bones are recognisable : — mastoid 8, tympanic 28, scptaraosal 27, malar 26, 
maxillary 21, premaxillary 22; the end of the long pterygoid is seen at 24, abutting 
against the lower end of the tympanic. But little of the composition of the mandible 
is discernible: the tightly closed jaws show the extent of the interlocking of the 
long, slender, curved, and sharp-pointed teeth. 
Of those of the lower jaw the crowns of upwards of twenty may be traeed ; the 
longest occupying the middle three fourths of the series, and the largest of these being 
the foremost. In some parts of the series two teeth pass into the same dental inter- 
spaee of the opposite jaw. 
The admirably wrought-out specimen figured in Tab. Ill, fig. 1, exhibits the upper 
surface of the somewhat crushed skull. Of the basi-occipital a part of the upper surfaee 
(l) and of the single median convex condyle is shown. The exoccipitals (ib., 2) preserve 
their connection with the lateral and upper parts of the basi-oceipital, and show the 
surfaces — seemingly sutural — from which the superoccipital (ib., 3) has been displaced. 
These surfaces (2, 2) are thick and triangular ; they are parallel with the middle of the 
foramen magnum, the lower half of which is formed by the basi- and ex-occipitals. 
From the outer and back part of the exoccipital the paroccipital process (4, 4) is 
continued ; of subtriedral form, long, slender, and tapering to a thin rounded apex : 
the outer side appears to be sutural, and that of the left side is applied to the tympanic 
(lb., 28) : the length of this process is 8 lines. The breadth of the occiput, outside 
of the exoccipitals, is 1 inch 5 lines ; that of the foramen magnum is 6 lines. That the 
rough triangular upper surfaces of the exoccipitals are natural, not the result of frac- 
